I can tell you how my early '99 was run, and I would be surprised if yours were not the same when stock. Actually, I'm going to be reminding myself how things were done as I write the post, because it has been awhile since I did this part.
[Edited to add: This is kind of long, and I don't cut to the chase until the end. So to summarize, AC outlets are run as a daisy chain type of circuit, i.e one feeds the next, feeds the next, feeds the next, etc.. The three you say are dead are the last three on the passenger side daisy chain, so that gives you a big clue. Okay, read on...]
[Okay, second edit: You say the three that don't work are the two in the upper passenger cabinet and then one over on the driver's side by the TV?! I don't think my rig ever had one there and I was thinking you mean the one over by the VCR hole on the passenger side. Can you let me know if it is the latter or if you did mean an outlet over by the TV on the driver's side? If so, then do you have one by the VCR hole and does that one work?]
First of all, all of the outlets (except the microwave) are on the same, single, "outlets" circuit, which is fed with 14AWG wire. Since your issue seems related to the "outlets" circuit, we'll concentrate on that. It starts at the brown box, then goes to the "master outlet," which is the GFCI outlet by the rear door/bathroom side. From there it turns into two main runs, one that goes up the driver's side (which we'll ignore for now), and one that goes behind the shower, then up over the door to the passenger side. The 14AWG wire that feeds the ones on the passenger side, runs over the rear door in the same loom as the Air-con 12AWG wire. These AC wires are all solid copper "Romex" type three-conductor wire. Here is how things look as they cross to "the other" (passenger) side over the door (a click should enlarge if necessary).
So, that loom continues along horizontally until it reaches the very back/passenger corner of the rig, behind the carpet that lines the closet. Then it goes vertically down in that corner to the floor, at which point it goes forward until it hits the generator box (which isn't far) at which point it goes up and runs over the top of the generator box (still by the outside wall, so this is just below the lower refrigerator vent). As it crosses the generator box it powers the AC outlet that the refrigerator is plugged into. Then it continues on (still taped together with the Air-con wire) and goes behind the stove wall and feeds the outside AC outlet. Then it goes vertically up the wall behind the stove....
When it gets to the place where the outside wall meets the lower roof "swoop" then it heads forward, into the main passenger side wire chase (which is on the outside wall just beneath the lower roof swoop). From there it branches twice into the false floor of the over-dining cabinets to feed the two outlets on the lower side of those. You can get to those outlets by removing the inner cabinet outside ends, then the little outside wall piece under the swoop, then any cabinet divider septum (can't remember if dining cabinet has one), then the false floor (all white screws pretty easy to undo).
After the cabinet outlets the wire run continues forward along the chase and around into the entertainment area, where there is an outlet facing forward behind the stile that divides the VCR area from the center door area. That's the end of that wire run.
So, since the last three outlets on that side are dead (I presume they act the same on shorepower or generator right? You specify generator but I can't think of how that would be different than shorepower under the original wiring scheme), then I would guess it's something after the outside outlet (does that work?). The three you describe as not working are the last three on the passenger side line.
Someone could have done some remodeling, I suppose, but that would be kind of weird without any other clues or obvious reason. Another thought: The outlets in my Concourse are typical RV "speed outlets," which you can look up online to see how they work on the back. Essentially, they are the box and the outlet in one, and the wires sort of plug in. I did have a previous camper van in which the original owners said one outlet had never worked since new. Turns out one of the wires was not correctly put into a speed outlet downstream, and once I found that and fixed it, they all worked just fine.. So you might check something like that.